As a method for improving fuel economy of the vehicle, there is a technique of the engine automatic-stop control that automatically stops the engine when predetermined conditions are satisfied, e.g. as one condition, a vehicle stop state in which there is no intention of starting the vehicle continues for a setting time at a vehicle stop.
In this engine automatic-stop control technique, when an operation which is considered as driver's intention to start the vehicle is performed, e.g. when a brake pedal is released and a braking state is changed from a working state to a non-working state, the engine is automatically restarted by cancelling the engine automatic-stop control.
Here, since the engine is not running during execution of the engine automatic-stop control, there is no hydraulic pressure from the engine-driven oil pump driven by this engine, and the transmission is in a state incapable of transmitting the power.
When the engine is started from this state by cancel of the engine automatic-stop control, the hydraulic pressure from the engine-driven oil pump driven by this engine start is generated, and the transmission becomes in a state capable of transmitting the power.
However, there is a delay of response to generate the hydraulic pressure by the engine-driven oil pump driven by the engine start and to bring the transmission to the power transmission-capable state, and this not only deteriorates a vehicle restart response, but also there arises a problem that a restart shock occurs due to engine RPM surge or engine flare-up or this adversely affects durability of the transmission.
Thus, as described, for example, in Patent Document 1, a technique which operates the electric oil pump instead of the engine-driven oil pump and keeps the transmission in the power transmission starting state by the working fluid from the electric oil pump, during execution of the engine automatic-stop control, has been proposed.
According to this technique, since the transmission is kept in the power transmission starting state by the working fluid from the electric oil pump even during execution of the engine automatic-stop control, the working fluid from the engine-driven oil pump is able to increase a transmission control pressure from a hydraulic pressure value generated by the electric oil pump to a hydraulic pressure value that brings the transmission to the power transmission-capable state instantly after the engine restart by the cancel of the engine automatic-stop control. Therefore, the transmission can transmit the power just after the engine start without an occurrence of slip, and the vehicle restart response can be improved, also the problem such as the occurrence of the restart shock and the adverse effect on the durability of the transmission can be resolved.
Here, upon failure of the electric oil pump, i.e. when the electric oil pump cannot generate a pump pressure nor increase the pump pressure as specified due to its own failure or failure of a power system or a control system, the transmission cannot be kept in the power transmission starting state during execution of the engine automatic-stop control, and not only a primary object such as the improvement of the restart response cannot be achieved, but also a great restart shock and the adverse effect on the transmission occur.
Thus, at the failure of the electric oil pump, it is desirable to forbid the engine automatic-stop control, which is mentioned in Patent Document 1 too.
A technique of forbidding of the engine automatic-stop control at the failure of the electric oil pump described in Patent Document 1 is a technique that judges the failure of the electric oil pump at the engine automatic-stop control, and permits the engine automatic-stop control then executes the automatic engine stop in a case of judgment of no failure, or forbids the engine automatic-stop control then does not execute the automatic engine stop in a case of judgment of the failure.